Re: [Cbor] Review of draft-ietf-cbor-packed-02

Russ Housley <housley@vigilsec.com> Mon, 15 March 2021 18:40 UTC

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From: Russ Housley <housley@vigilsec.com>
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Date: Mon, 15 Mar 2021 14:40:11 -0400
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To: Carsten Bormann <cabo@tzi.org>
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Subject: Re: [Cbor] Review of draft-ietf-cbor-packed-02
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Carsten:

> thank you for this review.
> 
>> Document: draft-ietf-cbor-packed-02
>> Reviewer: Russ Housley
>> Review Date: 2021-03-15
>> 
>> Major Concern:
>> 
>> RFC 7049 says that CBOR was designed so that "encoded data should be
>> self-describing so that a generic decoder can be written."  I di not
>> expect Packed CBOR to deviate from this design goal.  However, the
>> feature that allows an application environment, such as a media type,
>> to define tables does exactly that.  Decode will fail if these table
>> values are not known to the decoder.
> 
> Well, decode won’t fail, but unpacking will leave holes.
> That is a consequence of using external dictionaries that is hard to avoid.
> Would you prefer to rule out external dictionaries?  
> They sure were useful in places like RFC 3485 etc.

 I felt this point of divergence from the original design goal needed explicit discussion.

I'm not sure what the right answer might be.  Maybe some preamble to say that a named table is needed for successfully recovering the entire content. In the current document, this context is assumed.

Russ